Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Patients who consumed the amount of vitamin D contained in daily servings of milk and fish were 40 percent less likely to develop polyps than those who got little or no vitamin D.

The study also confirmed previous research that found that cereal fiber and regular use of pain relievers such as aspirin and ibuprofen reduce the risk of advanced polyps and that smoking, heavy drinking and a family history of polyps raise the risk.

Diets high in calcium have been linked with a reduced colon cancer risk, and vitamin D is needed to help the body absorb calcium. But evidence about any protective effect from vitamin D alone is sparse, said Dr. David Lieberman, the lead author and a gastroenterologist at the Portland, Ore., Veterans Affairs Medical Center.

The study appears in Wednesday's Journal of the American Medical Association.

It involved mostly men ages 50 to 75 who underwent routine colon cancer screening exams called colonoscopies between 1994 and 1997. The exams, in which a long flexible tube is snaked through the rectum into the entire large intestine, can detect and remove abnormal growths.

The American Cancer Society recommends the tests every 10 years starting at age 50 to help detect colorectal cancer, which is diagnosed in about 147,000 Americans each year.

Study participants filled out detailed health questionnaires before their exams asking about diet, family medical history and lifestyle habits. Participants were not asked about exposure to sunlight, which interacts with chemicals in the skin to produce vitamin D and is a major source of the vitamin.

Advanced polyps were found in 299 participants and colon cancer was detected in 30 participants.

Participants who reported consuming more than 645 international units of vitamin D daily were 40 percent less likely to have advanced polyps than those who consumed little or none of the vitamin. Experts generally recommend about 200 to 800 IUs of vitamin D a day for adults.

Food sources of vitamin D include some types of fish and fortified milk. For example, one tablespoon of cod liver oil has 1,360 IUs; 3 1/2 ounces of salmon have 360 IUs; and a cup of fortified milk contains 100 IUs.

Supplements are frequently combined with calcium and often contain at least 200 IUs, Lieberman said.

Dr. David Beck, chairman of colorectal surgery at the Ochsner Clinic Foundation in New Orleans, said the link between vitamin D and reduced risk of polyps is not surprising. Beck, however, questioned how accurately the researchers were able to assess people's vitamin intake since they relied on questionnaires rather than giving participants vitamin D-rich foods or supplements.

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